Abstract/Summary

For many decades molluscan data have been critical to the establishment of the concept of a global-scale increase in
species richness from the poles to the equator. Low polar diversity is key to this latitudinal cline in diversity. Here we
investigate richness patterns in the two largest classes of molluscs at both local and regional scales throughout the Southern
Ocean. We show that biodiversity is very patchy in the Southern Ocean (at the 1000-km scale) and test the validity of
historical biogeographic sub-regions and provinces. We used multivariate analysis of biodiversity patterns at species, genus
and family levels to define richness hotspots within the Southern Ocean and transition areas. This process identified the
following distinct sub-regions in the Southern Ocean: Antarctic Peninsula, Weddell Sea, East Antarctic—Dronning Maud
Land, East Antarctic—Enderby Land, East Antarctic—Wilkes Land, Ross Sea, and the independent Scotia arc and sub
Antarctic islands. Patterns of endemism were very different between the bivalves and gastropods. On the basis of
distributional ranges and radiation centres of evolutionarily successful families and genera we define three biogeographic
provinces in the Southern Ocean: (1) the continental high Antarctic province excluding the Antarctic Peninsula, (2) the
Scotia Sea province including the Antarctic Peninsula, and (3) the sub Antarctic province comprising the islands in the
vicinity of the Antarctic Circumpolar Current.